Electronic structure changes across the charge density wave transitions in LaAgSb₂

Ashish Atma Chainani^1*, J.H. Li^1,2, A. Singh¹, Y.F. Liao¹, Y.Y. Chu¹, K. D. Tsuei¹, D. J. Huang^1,2, C.N. Kuo³, C. S. Lue³

¹Condensed Matter Physics, NSRRC, Hsinchu, Taiwan
²Physics, NTHU, Hsinchu, Taiwan
³Physics, NCKU, Tainan, Taiwan

* Presenter:Ashish Atma Chainani, email:chainani.ash@nsrrc.org.tw

We study the electronic structure of LaAgSb₂, using bulk sensitive temperature dependent (20 K – 220 K) Hard X-ray photoemission spectroscopy (HAXPES). LaAgSb₂ exhibits two charge-density-wave (CDW) transitions, one below T₁ = 207 K with a modulation wave vector (0.026,0,0) along the crystallographic a-axis, followed by a second CDW transition below T₂ = 186 K along the c-axis with a modulation vector (0,0,0.16), accompanied with weak kinks in the electrical resistivity [1-3]. Recent studies have identified a Dirac-cone band dispersion in LaAgSb₂ and nested Fermi surfaces at a low temperature of T = 16 K, but temperature dependent measurements were not reported[4]. We use a bulk sensitive spectroscopy technique to investigate temperature dependent changes in the electronic states of La, Ag and Sb in order to identify states responsible for the CDW transition in LaAgSb₂. Temperature dependent HAXPES core level measurements show that the La 3d and Ag 3d core-levels show negligible changes across the CDW transitions. In contrast, temperature dependent measurements show a clear well-separated satellite of the Sb 3d core levels below T₁, and the spectral intensity of the satellite progressively increases on lowering the temperature below T₂. The temperature dependence of the Sb 3d satellite feature suggests a second order transition, consistent with the known BCS behavior of temperature dependent superlattice reflections by x-ray diffraction[3]. The valence band spectra also indicate a purely anionic character CDW transition, with no involvement of the La and Ag cationic derived states.

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Keywords: charge density wave, strongly correlated system, hard x-ray photoemission spectroscopy